This invention relates to a relief valve.
JP-A-H8-42513 published in 1996 by the Japanese Patent Office discloses a relief valve included in the flow control valve of a power steering device.
FIG. 10 shows this flow control valve 200. A relief valve 250 is incorporated in a spool 201 of the flow control valve 200, as shown in the diagram.
Oil supplied to a supply chamber 202 at the tip of the spool 201 from the pump port P is supplied to the power steering device via an orifice 203 and an oil supply port 204.
The oil pressure on the side of the oil supply port 204 (oil pressure downstream of the orifice 203) is introduced to a flowrate control spring chamber 205 at the base end of the spool 201. The spool 201 displaces under a balance between a thrust force due to the oil pressure of the supply chamber 202 and the supply port 204 (oil pressure both upstream and downstream of the orifice 203), and a reaction due to the spring force of a spring 206 provided in the flow rate control spring chamber 205 and the oil pressure of the flowrate control spring chamber 205. When the differential pressure upstream and downstream of the orifice 203 increases due to an increase of the pump rotation speed, the thrust force due to the oil pressure of the supply chamber 202 exceeds the reaction force, the spool 201 displaces in the base direction (left-hand direction of FIG. 10), and the supply chamber 202 communicates with a tank port T. Therefore, part of the flowrate from the pump port P is returned to the tank, and the flowrate is controlled.
When the load on the power steering device increases and the oil pressure of the oil supply port 204 sharply increases, if the oil pressure of the pressure control spring chamber 205 exceeds the set pressure of the relief valve 250, the relief valve 250 is pushed open, and oil in the pressure control spring chamber 205 escapes to the tank port T. As a result, the spool 201 displaces in the base end direction, oil pressure in the supply chamber 202 escapes to the tank port T, and the supply pressure is prevented from increasing beyond the permitted pressure.
However, in the aforesaid relief valve 250, there is a large gap between a ball support member 252 which supports a ball 251, and the inner circumference of a valve hole 253, so movable members (the ball 251 and ball support member 252) easily vibrate in a side direction (radial direction) due to the effect of the inclination of a return spring 254 and the side force of the flow when the relief valve 250 opens.
Further, in this relief valve 250, in a transient state when the movable members are pushed open, noise is produced by chattering which makes the operation of the movable members unstable. If the diameter of a seat orifice 255 is reduced, this chattering can be suppressed, but in this case pressure losses increase, and override characteristics of the relief valve 250 (characteristics of the difference between a set pressure and a cracking pressure) are impaired.
It is therefore an object of this invention to stabilize the operation of movable members, prevent chattering and improve override characteristics in a relief valve.
In order to achieve the above object, this invention provides a relief valve, comprising a valve seat comprising a seat hole, a ball which opens and closes the seat hole from the downstream side, a movable member which supports the ball from the downstream side, a housing part which houses the movable member, and an orifice formed downstream of the seat hole which damps the vibration of the movable member and suppresses chattering by restricting an oil flow.
According to an aspect of this invention, this invention provides a flowrate control valve which controls the flowrate supplied from a pump to a load circuit comprising a relief valve, the relief valve comprising a valve seat having a seat hole, a ball which opens and closes the seat hole from the downstream side, a movable member which supports the ball from the downstream side, a housing part which houses the movable member, and an orifice formed downstream of the seat hole which damps the vibration of the movable member 4 and suppresses chattering by restricting an oil flow. The relief valve opens when the pressure on the load circuit side rises, and part of the fluid from the pump is discharged to a tank port.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.